Comparison of UV and ELS detectors in HSPEC analysis of natural organic matter in dam water

Authors

  • KG Moodley Department of Chemistry, Durban University of Technology, PO Box 1334, Durban, 4000, South Africa
  • P Sobantu Department of Chemistry, Durban University of Technology, PO Box 1334, Durban, 4000, South Africa
  • G Gericke Eskom RT & D, Lower Germiston Road, Rosherville, Gauteng, South Africa
  • DK Chetty Department of Chemistry, Durban University of Technology, PO Box 1334, Durban, 4000, South Africa
  • DH Pienaar Department of Chemistry, Durban University of Technology, PO Box 1334, Durban, 4000, South Africa

DOI:

https://doi.org/10.4314/wsa.v43i3.17

Keywords:

Natural organic matter, dam water, determination, ELSD

Abstract

This project arose out the need for a simple method to analyse natural organic matter (NOM) on a routine basis. Water samples were obtained from the Vaal Dam. Analysis was preceded by separating the NOM into the humic and non-humic fractions. The humic portion was separated further into two fractions by employing a non-ionic DAX-8 resin to separate humic acid from fulvic acid. High-performance size-exclusion chromatography (HPSEC), equipped with a UV detector and an evaporative light scattering detector (ELSD) was used to obtain information on the molecular weight distribution and concentration levels of the two acids. Mixed standards of polyethylene oxide/glycol were employed for calibration. The molecular weight distributions (MWDs) of the isolated fractions of humic and fulvic acids were determined with ELSD detection as weight-average (Mw), number-average (Mn) and polydispersity (ρ) of individual NOM fractions. The Mw/Mn ratio was found to be less than 1.5 in all fractions, indicating that they have a low and narrow size fraction. It is noted that the ELSD detector proved to be far more capable than the UV detector. A finding of interest is that 40% of the total organic carbon in the dam water samples could be attributed to humic substances. The developed method successfully separated the humic substances from water and further separated the humic substances into the component acids, namely, humic and fulvic acids. Molecular weight distribution of these compounds is a powerful indication of how much DOM was present in the dam water. Even though the UV method was useful in characterizing these substances, the ELS detector is recommended because it detects all the organic species present.

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Published

2017-07-28

Issue

Vol. 43 No. 3 July (2017): Water SA

Section

Research paper

License

Copyright (c) 2017 KG Moodley, P Sobantu, G Gericke , DK Chetty, DH Pienaar

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This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

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The content of this journal is licensed under a Creative Commons Attribution Licence.  Users are permitted to read, download, copy, distribute, print, search or link to the full texts of the articles in this journal under the terms of this Licence, without asking prior permission from the publisher or the author, provided the source is attributed. Copyright is retained by the authors.

How to Cite

KG Moodley (2017) “Comparison of UV and ELS detectors in HSPEC analysis of natural organic matter in dam water”, Water SA, 43(3 July). doi:10.4314/wsa.v43i3.17.